In the state of the art there are various known compounds used to inhibit the degradation of packaged substances caused by the oxidation reactions triggered by the oxygen located at the head space of the packages or that permeate through the packaging material. These types of substances are usually called oxygen absorbers or sweepers.
Various sweeper oxygen absorber compounds have been developed, including organic and non-organic variations, which, in some case, need to be in the presence of a catalyst or a substance that triggers the absorption reaction.
Among the non-organic compounds, there are substances made out of iron, for example metal salts and dust. These substances are mentioned in the U.S. Pat. Nos. 5,143,763 and 5,928,560. The traditional use of these compounds is developed by inserting them in little air-permeable envelopes (“sachets”) inside of the packaging of dry products, preventing direct contact between the compounds and the packed product. This form of use carries the risk of contaminating the product due to the possible breaking of the envelopes or even its ingestion.
These problems, even for the liquid or moisturizing products, could be solved by soaking the compounds inside the wall of the package, when it is possible to react to the oxygen that filters through the walls. This solution is not possible for these non-organic compounds and, nonetheless, it has represented a possible idea regarding organic compounds.
The organic substances that fulfill the oxygen absorption role, like ascorbic acid, ascorbates, isoascorbates, ascorbyl palm itate, salicylic acid and their derivative substances, need to be in contact with a salt to form compounds that trigger an oxygen absorption, in which the salt generally comes from a transition metal. Details and examples of these absorbing substances can be found in the U.S. Pat. Nos. 4,524,015, 6,465,065, 6,274,210 and 6,656,383.
There are patents that have claimed oxygen-sweeping organic compounds, with or without catalysts, incorporated in polymer matrixes, like the U.S. Pat. No. 5,364,555 and the Japanese patent applications 61-238,836 and 54-022,281. Nonetheless, these organic compounds have two conditions that need to be taken into account. On the one hand, by reactions directly or indirectly with oxygen and by its own nature, they would cause reaction products that could affect the package's structure that could also disturb the packed product itself, diminishing its quality. On the other hand, for assuring and improving its efficiency they have to be protected from the effects caused by temperature or UV radiation.
For example, the degradation of ascorbic acid and its derivatives caused by its reactions to oxygen, temperature and UV radiation have been widely studied, and it can produce unpleasant colors and smells (Commission of the European Communities, 2001) (Giorgia Spigno, 1999) (Jeane Santos de Rosa, 2007) (Kurata & Sakurai, 1967) (Pascault, Sautereau, Verdu & Williams, 2002) (Santos, 2008).
In U.S. Pat. No. 5,364,555, the claim regards an oxygen-sweeping compound that contains salicylic acid chelate or a compound made of the same transition metal or a metal salt, which can be incorporated into a polymeric matrix as PVC. Nonetheless, nor the method by which the oxygen sweeper is incorporated into the matrix or the way in which the product of the reaction between salicylic acid and oxygen is prevented from reaching the packed product are specified. In fact, the formulation that was revealed refers to the manufacturing of liners that adhere to the lids or the seal of the products instead of sticking to the packages that hold the oxygen absorber.
Japanese application 61-238,836 shows a film for structures of packaging made from a thermoplastic material such as low-density polyethylene (“LDPE”), that includes ascorbic acid by itself or combined with aliphatic polycarboxylic acids. Although the fact that the film shows good properties regarding gas barriers is clearly stated, the application does not show the method by which the ascorbic acid is protected from a premature degradation in the making of the film or the way in which the products of the oxidation of the acid is prevented from reaching the packaging or the product itself.
In the same way, the Japanese application 54-022,281 displays a fruit tray made out of thermoplastic foam a thin layer of ascorbic acid or erythorbic acid (or any of its alkaline salts), put over the tray's slots. Regardless, there are some doubts involving the products of the oxidation of these compounds and how to manage for them not to reach the packed fruit.
U.S. Pat. No. 5,977,212 claims a composition in which the sweepers are contained in an inert-porous matrix that could hold the reaction's products and protect it from thermal effects during the process developed with the polymer matrix. However, this patent does not state the method in order to get said results, nor it specifies the effect the effect that the matrix has on the oxygen absorption kinetics. The same happens in U.S. Pat. No. 6,458,438, where the claim consists of a polymeric film that holds the oxygen absorber within a zeolite matrix.
The sol-gel method has been used for other purposes besides packaging, for example, for the encapsulation of active biological material and substances like lipids, membranes, proteins, enzymes, inks and carotenoid in porous materials like silicon dioxide or zeolites. This type of encapsulation has been divulged by the U.S. Pat. Nos. 5,200,334, 6,767,483 and 6,495,352, and also by the following documents:    M. Mureseanu, A New Mesoporous Micelle-Templated Silica Route for Enzyme Encapsulation, 34296 Montpellier Cedex 5, France, 2005.    J. W. Gilliland, Solvent Effect on Mobility and Photostability of Organic Dyes Embedded inside Silica Sol Gel Thin Films, University of Oklahoma, Norman, Okla. 73019, 2005.    Z. He, Carotenoids in Sol Gels: Incorporation, Stability, and Sensitivity to Oxidant and Acid, Tuscaloosa, Ala. 35487-0336, 2000.    M. Saenz, Estudio de las Variables de Reaccióen Sintesis de Silica Gel absorbente, Revista de Ingenierie e Investigación, Vol. 27 No. 2, August 2007.
Nonetheless, there is no known application that involves the sol-gel reaction and the oxygen sweepers for its incorporation in packaging technology in the prior state of the art.